Conventional Ndt Services

Holiday Inspection/Sponge Test

High Voltage / Low Voltage

Holiday test or a Continuity test is one of the Non Destructive Test method applied on protective coatings to detect unacceptable discontinuities such as pinholes and voids. The test involves checking of an electric circuit to see if current flows to complete the electrical circuit.
A Holiday test or Continuity test is performed by applying low voltage (connected in series with an LED or noise-producing component such as a piezoelectric speaker) across the chosen path. If the electrical flow is detected then the test area is termed as conductive indicating presence of discontinuities such as pinholes and voids. Three types of commercially manufactured electrical holiday detectors are readily available to the industry. The low voltage (wet sponge) type of holiday detector which is applicable for use on high dielectric protective coating with maximum dry film thickness of 20 mils (.51 mm) and both pulsating & continuous DC high voltage (spark type) holiday detectors that can be used successfully on high dielectric strength protective coating with dry film thickness' ranging from a few mils to fractions of an inch.

An electrical holiday detector is a device which locates areas or points on a coated conductive concrete substrate where there is a great difference in electrical resistance between the exploratory electrode on the coated surface and the underlying structure. The fact that most protective coatings used on concrete structures are highly resistant to a flow of electrical current makes this method of testing quite practical.


  • It is fairly easy to use and extensive training is not required.
  • It is a non-destructive test.
  • The wet sponge is low cost.